Load tap changers for transformers



March 30, 1965 A. BLEIBTREU ETAL 3,175,089

LOAD TAP CHANGERS FOR TRANSFORMERS Filed June 19, 19 62 5 Sheets-Sheet 1Wyn/r0425.- WW WWW March 30, 1965 A. BLEIBTREU ETAL LOAD TAP CHANGERSFOR TRANSFORMERS 5 Sheets-Sheet 2 Filed June 19, 1962 41 f/A/mvroes 0mmWM 1, WWW b March 30, 1965 A. BLEIBTREU ETAL 3,176,089

LOAD TAP CHANGERS FOR TRANSFORMERS Filed June 19, 1962 5 SheetsSheet 3/NVEN7'O,PS

EMMA Wm WM 4mm March 30, 1965 A. BLEIBTREU ETAL 3,176,089

LOAD TAP CHANGERS FOR TRANSFORMERS Filed June 19, 1962 5 Sheets-Sheet 4lurzwrops WW Mm WMM m M VA/WW im W Mamh 1965 A. BLEIBTREU ETAL 3,175,039

LOAD TAP CHANGERS FOR TRANSFORMERS Filed June 19, 1962 5 Sheets-Sheet 5WW1. MAM WM KW M. M WW XWW United States Patent LOAD TAP CHANGERS FORTRANSFORMERS Alexander Bleibtreu, Regensburg, Germany, and Anton AugustSchunda, deceased, late of Regensburg, Germany, by Wilhelmine Schunda,Anton Schunda, and

Brunhilde Schunda, heirs, all of Regensburg, Germany,

assignors to Maschinenfabrik Reinhausen (lehruder Scheubeck K.G.,Regensburg, Germany, a firm of Germany Filed June 19, 1962, Ser. No.204,029 Claims priority, application Germany, June 22, 1961, M 49,421 8Claims. (Cl. 200-18) This invention has reference to load tap changersfor power transformers as applied, for instance, to maintain a constantsecondary voltage with a variable primary voltage, to control the flowof reactive kva. between two generating systems, and to control thedivision of power between branches of loop circuits, etc.

It is a general object of this invention to provide improved load tapchangers for polyphase transformers, in particular polyphase highvoltage power transformers.

A further object of this invention is to provide load tap changers forpolyphase high voltage power transformers which are considerably morecompact, and involve considerably smaller manufacturing cost, thancomparable prior art load tap changers.

Load tap changers include selector switches and transfer switches. Theselector switches serve the purpose of selecting a particular tap on atapped transformer winding intended to be connected into an electriccircuit. Selector switches do not carry any load currents at the time aparticular tap is selected, i.e. they are not required to interrupt orclose on current-carrying circuits. This task is performed by thetransfer switches. The latter perform all switching operations underload. Therefore all arcing is restricted to the transfer switches, theselector switches merely selecting the particular transformer tap towhich the load is to be transferred.

Polyphase transformers require a selector switch and a co-operatingtransfer switch for each phase of the circuit. The selector switch andthe transfer switch of each phase must be electrically insulated fromthe selector switch and the transfer switch of each other phaseaccording to the full voltage between phases. For this reason it hasbecome common practice to subdivide polyphase transformers into separatetransformer units. Each such single phase unit comprises a separatetank, a separate single phase transformer, a separate load tap changer,and a separate drive for the latter. A plurality of such single phaseunits are integrated into a transformer bank. Transformer banks tend tobe extremely bulky.

It is, therefore, another object of this invention to provide load tapchangers which are less bulky than the load tap changers normallyassociated with transformer banks including a plurality of separatesingle phase transformer units.

It is frequently possible to reduce the aggregate size of a polyphasetransformer including load tap changing means by arranging all thephases of such a transformer and the selector switches and the transferswitches of all the phases in a common tank. Where the voltage of agiven polyphase transformer is high and its power large, the size ofsuch transformers and of their associated load tap changing means tendsto become intolerably large, and often exceeds the bulk limits requiredfor transportation via rail, i.e. on railroad cars.

It is, therefore, another object of this invention to provide polyphasehigh voltage load tap changers which lend themselves to be combined withpolyphase transformers whose various phase windings are arranged in acommon "ice tank, i.e. built into the common tank, which load tapchangers are extremely compact and add relatively little to the bulk ofthe composite transformer and load tap changer unit.

In the method of tap changing a current limiting device must be employedduring each transition period from one tap position to the other. Suchcurrent limiting devices may either be center tapped reactors orresistors. This invention is particularly concerned with load tapchangers wherein resistors are used as current limiting devices.

Load tap changers utilizing resistors as current-limiting devices andfast operating transfer switches are known, or referred to, as Jansentype load tap changers. This type of load tap changers has importantadvantages over load tap changers of other kinds. In this type of loadtap changers the current-limiting resistors are in parallel with respectto the load current and in series with respect to the circulatingcurrents which flow during transition times between tap changes. Thismakes it possible to reduce the resistance of the current limitingresistors to relatively low ohmic values without giving rise to largecirculating currents. In Jansen type tap changers the movable contactsof the transfer switches move at high speeds, or with a snap action,wiping over the fixed contacts to which the current limiting resistorsare connected. As a result of this fast motion the transition periodsduring which the current limiting resistors must carry load currents arevery short, say in the order of a few hundredths of a second. This hastwo significant advantages: The current limiting resistors can be madevery small and the voltage fluctuation resulting from tap changesinsignificant. The rapid operation of the transfer switches is producedby stored energy means, preferably wound up springs which are maintainedin a pre-wound, or pre loaded, condition in readiness for the next tapchanging operation. Load tap changers of the Jansen type are well knownin the art and have been described in many printed publications such as,for instance, the book by H. P. Young, Electric Power Control Systems,London, England, Chapman 8: Hall Ltd, 1942, and reference may be had tosuch publications for a more complete description of Jansen type loadtap changers, and the structural features and operating characteristicsthereof.

It is another object of this invention to provide improved lansen typeload tap changers for polyphase high voltage power transformers.

The foregoing and other general and special objects of the invention andadvantages thereof will appear more clearly from the ensuing particulardescription of the invention as illustrated in the accompanyingdrawings, wherein:

FIGS. la and lb are substantially a vertical section of a high voltagepolyphase load tap changer embodying the present invention andcomprising a plurality of selector switches, a plurality of transferswitches cooperating with the selector switches and drive meaens forboth the selector switches and the transfer switches, FIG. 1a showingthe left portion of the structure and FIG. 1b showing the right portionof the structure, both FIGS. 1a and 1b being complementary, FIG. lashowing at the right side thereof some structural detail which is alsoshown in FIG. lb to the left side thereof;

FIG. 2 is a top plan view of one of the selector switches and of one ofthe transfer switches of the structure of FIG. 1;

FIGS. Zia-3c are top-plan views of the three transfer switches of thestructure of FIG. 1; and

FIG. 4 is a connection diagram of one phase of a polyphase transformerprovided with a load tap changer embodying the present invention.

Referring now to the drawings, the structure shown in FIGS. 1 and 2 isintended to be accommodated within a en /spec transformer tank having acover on the top thereof. Neither the transformer tank nor the tankcover have been shown in FIG. 1. The cover of the tank of thetransformer defines an opening which is covered by a part which may bereferred to as a sub-cover. Reference numeral 115 has been applied inFIG. 1 to indicate the aforementioned sub-cover. Sub-cover 19 supports avessel 11 of insulating material including a bottom 12. The lateralwalls of vessel 11 are formed by an insulating cylinder or tube aswidely applied in high voltage engineering. Vessel 11 is filled with anappropriate insulating liquid such as insulating oil. The bottom 12 ofvessel 11 is provided with an opening 13 normally closed by a screw fordraining oil from vessel 11. Tubular switch support 14 is arrangedinside of vessel 11 in coaxial relation thereto. Support 14 is made ofinsulating material and houses three transfer switches 15, 16 and 17which are arranged in coaxial relation to each other and to support 14and vessel 11 and stacked one above the other. Transfer switches 15, 16,17 are of the rotary type and are mounted on, and operated by, a commonshaft 18 adapted to insulate each transfer switch from the others. Asclearly shown in PEG. 2 each transfer switch comprises a set or group ofmovable contacts 19 adapted to cooperatively engage a set or group ofcircularly arranged fixed contacts 21. The set or group of contacts 19is pivotally supported at 19a on a rotatable contact carrier 20.Contacts 19 are arranged along a sector of a circle whose center 19a isspaced from the axis of rotation of contact carrier 20. The fixedcontacts 21 are supported on the inner surface of the aforementionedinsulating cylinder or insulating tube 14. When contact carrier 20 andmovable contacts 19 are operated, fixed contacts 21 are sequentiallyengaged by movable contacts 19, the latter performing a composite rotaryand radial motion as set forth more in detail in US. Patent 2,680,790 toB. Jansen. The two movable contacts 19 on both ends of the sector ofmovable contacts 19 are main contacts, and the intermediate contacts ofthe sector of movable contacts 19 are switch-over contacts. In a likefashion the two contacts on both ends of the sector of fixed contacts(indicated in some of the figures by reference character 22) 21 are maincontacts and the intermediate contacts of the sector of fixed contacts21 are switch-over contacts (indicated in some of the figures byreference character 23). The aforementioned fixed main contacts 21 areconductively connected to the particular tap of the transformer windingwhich has been selected, while the aforementioned fixed switch-overcontacts 21 are conductively connected to switch-over resistors ortap-changing resistors 24 in the fashion shown in FIG. 4.

Each transfer switch 15, 16, 17 comprises in essence three sector-shapedspaces of which one is occupied by the set of movable contacts 19 andthe two others 25 are occupied by the aforementioned switch-over ortap-changing resistors 24. The location of the latter has been clearlyshown in FIG. 2 as well as in FIGS. Zia-3c.

The carriers 20 for the movable contacts 19 are secured to compositeshaft 18. This shaft comprises tubular sections 26 of insulatingmaterial alternating with sections formed by metal rods 27. Each of thetwo sections formed by metal rods 27 is interposed between a pair ofsections 26 of tubular insulatin material. The latter sections 26separate and insulate each transfer switch 15, 16, 17 from the transferswitch or transfer switches immediately adjacent thereto.

Reference character 28 has been applied to indicate annular members forcontrolling the voltage distribution, i.e. the distribution of theelectric field, around transfer switches 15, 16, 17 along parts 11 and14. At least two such voltage control members 28 are anranged at eachaxial end of each transfer switch 15, 16, 17. As shown in FIG. 1 some ofthe voltage distribution control 23 are arranged inside of insulatingtubing 14 and su ported by the latter, and others are arranged outsideof vessel 11 and are supported by the latter. All of th voltagedistribution control rings 28 are arranged in coaxial relation to parts11, 14 and 18.

Since contacts 19 and 21 of transfer switches 15, 16, 17 part whilecarrying load currents arcs are kindled between these contacts incidentto parting thereof, and these arcs form hot, ionized products of arcing.In order to avoid discharge of hot products of arcing formed in lowertransfer switches to the arcing zones of the transfer switches arrangedat a relatively higher stack level, transfer switches 15, 16, 17 areangularly displaced. In three phase transformers comprising threetransfer switches 15, 16, 17-one for each phase-the angular displacementof the three transfer switches is degrees. This has been shown in FIGS.3a3c of which each figure is a horizontal section at right angles toshaft 18 and of which each figure shows in top-plan view one of thethree transfer switches 15, 16, 17.

Transfer switches 15, 16, 17 are operatively related to rotary selectorswitches 30, 31 and 32, i.e. transfer switch 15 is operatively relatedto selector switch 39, transfer switch 16 is operatively related toselector switch 31 and transfer switch 17 is operatively related toselector switch 32. Selector switches 30, 31 and 32 are stackedsubstantially in the same fashion as transfer switches 15, 16 and 17.Transfer switch 15 and selector switch 36 are arranged substantially atthe same level, transfer switch 16 and selector switch 31 are arrangedsubstantially at the same level, and transfer switch 17 and selectorswitch 32 are arranged substantially at the same level. The threeselector switches 30, 31 and 32 are mounted on a common tubularinsulating shaft 29. Switches 15 and 30 are arranged in the same phaseof a three phase circuit, e.g. phase U. In a similar fashion switches 16and 31 are arranged in the same phase of a three phase circuit, e.g.phase S. Finally switches 17 and 32 are arranged in the third phase orphase T of a three phase circuit. Switches 15 and 39 are interconnectedby relatively short, substantially horizontal leads 33, switches 16 and31 are interconnected by relatively short, substantially horizontalleads 34 and switches 17 and 32 are interconnected by relatively shortand substantially horizontal leads 35.

Each selector switch 30, 31, 32 comprises a plurality of fixed radiallyouter contacts 36 of which each is secured to an insulating rib 37.Fixed contacts 36 are adapted to be cooperatively engaged by the twobridge elements or bridge contacts 38 which may be turned about thecenter of a circle along which fixed contacts 36 are positioned. Thecurrent-carrying bridge elements or bridge contacts 38 are mounted oninsulating tube 29. Insulating tubes 39 extend parallel to insulatingtube 29i.e. both are vertical-and the latter support slip rings 49clearly shown in FIG. 2 for connecting fixed leads to rotary bridgecontacts 33. As shown in FIG. 1 annular members or rings 41 are arrangedabove each fixed contact 36 of each selector switch 30, 31, 32 forcontrolling the voltage distribution in the region of contacts 36.Annular metal members or rings 28 for the control of the voltagedistribution in axial direction are also arranged on the top and at thebottom of the stack formed by the three selector switches 30, 31, 32.

Insulating tubes 39 integral with the stack of selector switches 30, 31,32 are operable by means of a Geneva gear 42 shown in FIG. 1 arrangedabove the stack of selector switches 30, 31, 32. Geneva gears are widelyapplied in the art for operating selector switches of load tap changersand, therefore, Geneva gear 4-2 provided at the top of the stack ofselector switches 311, 31, 32 does not call for a detailed description.Gear train 43 arranged above Geneva gear 42 is provided for operatingthe latter. Gear train 43 is operated from a shaft 45 by theintermediary of a transmission which may include a clutch or coupling44. Shaft 45 is driven by an electric motor (not shown) which drivesalso the three transfer switches 15, 16, 17 shown to the left of FIG. 1.This is achieved by means of gear 46 and an eccentric 47 operating alink or rod 48 loading a spring 49 upon rotation of shaft 45. Referencenumeral 50 has been applied to indicate a tripping latch for releasingspring 49 when the particular taps intended to be inserted into the loadcircuit have been selected by means of the three selector switches 31 31and 32. Operation of the latch 50 results in an instantaneous movementof the current carrying contacts 38 of the three transfer switches 15,16, 17 from their original positions to their pre-selected positions.Operation of the three transfer switches 15, 16, 17 by spring 49 iseffected by the intermediary of an eccentric to which referencecharacter 51 has been applied. The aforementioned drive comprisingspring 49 and the transmission means for loading the same and fortripping the same are arranged within a gear housing 52 which is mountedon top of horizontal plate or cover on the top of the transformer tank.Gear housing 52 is provided on the upper side thereof with an opening orwindow 53 making it possible to readily determine the particularposition of the stack of transfer switches 15, 16, 17 and to inspect theconstituent parts or elements of the drive housed within gear housing52.

Referring now more particularly to FIG. 4, this figure shows to the leftthereof three windings 100 of a polyphase transformer. All threewindings 100 pertain to the same phase-say phase U-and only the centerwinding 100 is tapped. The center winding 1% has ten taps of which eachis connected to one of the ten fixed contacts 36 of one of the selectorswitches, say selector switch 30. In order to make it clear that thecenter windings of the other phases S, T are also tapped and alsoconnected to selector switches in the same fashion as the center windingof phase U, the reference characters 31 and 32 have been added inparentheses in FIG. 4 after reference character 30. The FIGURES 1 to 10at the left of FIG. 4 have been applied to distinguish between the tenfixed contacts 36 of selector switch 30. Transfer switch has been shownto the right of the selector switch and reference characters 16 and 17have been added in parentheses after reference character 15 to indicatethat the transfer switches 16 and 17 are related in the same fashion toselector switches 31 and 32 as transfer switch 15 is related to selectorswitch 30. Each transfer switch 15, 16, 17 is provided with six fixedcontacts 21 of which each of the four inner contacts 21 is connected toone of four tap changing resistors 24. The latter are, in turn,connected to the rotary contacts 38 of selector switches 30, 31, 32 bythe intermediary of leads 33, 34, 35.

Reference numeral 54 has been applied to indicate a reversing switch ofthe kind widely applied in connection with load tap changers. Reversingswitch 54 comprises a fixed center contact K and four additional fixedcontacts A, A, B, B. Lead 101 connects the lower terminal of the uppertransformer winding 160 to the fixed contact A of the reversing switch54 and lead 102 connects the upper terminal of the lower transformerwinding 100 to the fixed contact B of the reversing switch 54. Fixedcontacts A and B of reversing switch 54 are connected by leads 103 and103a to the upper terminal of transformer center winding 10%. Fixedcenter contact K of reversing switch 54 is connected by lead 104 to thesupport 20 of movable contacts 19 of the transfer switch 15. In theposition of the reversing switch 54 shown in FIG. 4, the fixed contactsA and A are conductively interconnected by movable contacts C and thefixed contacts K and B' are conductively interconnected by the movablecontact D. The current path of phase U shown in FIG. 4 is as follows:upper transfer winding 100, lead 101, fixed contact A, movable contactC, fixed contact A, lead 103, center winding 10!), fixed contact ofselector switch 39 at tap number seven, bridge contact 38, slip ring 40,lead 33, lead 105, upper fixed contact 6 21 of transfer switch 15,movable contact 19 of transfer switch 15 engaging the aforementionedfixed contact 21 thereof, contact support 20, lead 104, fixed contact Kof reversing switch 54, movable contact D, fixed contact B, lead 102,lower transformer winding 190.

In the embodiment of the invention shown in FIGS. 1, 2 and 3a, 3b, 30each transfer switch comprises but one single substantiallysector-shaped set of movable contact fingers 19 and one single set offixed circularly arranged contacts 21 cooperating with contact fingers19. Where prevailing current intensities are very large it may benecessary, or desirable, to provide each transfer switch 15, 16, 17 withmore than one substantially sector-shaped set of movable finger contacts19, and with an equal number of sets of fixed circularly arrangedcontacts 21. The aforementioned sets of movable and fixed contacts areconnected in parallel into each phase of a polyphase circuit, thuslimiting the current carrying duty which must be assigned to each singleset of contacts. In such a plural contact set arrangement there is lessroom within the space occupied by the transfer switches 15, 16, 17 foraccommodating tap changing resistors 24.

According to FIG. 4 tap number seven is included in the circuit of thetransformer and the load tap changer thereof. Assuming now that it isdesired to change from tap number seven to tap number eight. Such achange involves the following steps to be carried out in the followingsequence: Contact 38 which, heretofore, has been in engagement with thefixed selector switch contact number six is moved from the latterposition into engagement with fixed selector switch contact numbereight. This change of position of one of contacts 38 of each selectorswitch 30, 31, 32 does not involve the flow of any circulating currents.Nor does it involve any change in regard to the active windings of thetransformer. Concomitant with the aforementioned change of the positionone of contacts 38 of each of the selector switches 30, 31, 32 thespring 49 for instantaneous or snap-action operation of transferswitches 15, 16, 17 is loaded, and thus readied to effect aninstantaneous operation of said transfer switches. Upon tripping oflatch 50 the movable set of contacts 19 of each selector switch 15, 16,17 perform a composite or rolling motion thereby sequentially engagingthe fixed contacts 21 thereof. As a result of this motion the followingswitching operations are performed sequentially. The upper tap changingresistor 24 of FIG. 4 is inserted into the circuit, the two uppertap-changing resistors 24 of FIG. 4 are inserted into the circuit, thetwo tap changing resistors arranged in the center of FIG. 4 shunt thepart of center winding 1% situated between taps number seven and numbereight for a very short period of time, the two lower tap-changingresistors 24 of FIG. 4 are inserted into the circuit, but the lowesttapchanging resistor of FIG. 4 is inserted into the circuit, and finallyonly the lowest of movable contact 19 engages the lowest fixed contact21 providing a direct current path not including any of the tap-changingresistors 24. At this point of the tap changing operation contact 38engaging fixed contact 36 of tap number seven does not carry any currentany longer, all the current being carried by the other contact 38 inengagement with fixed contact 36 of tap number eight.

The next operation of the load tap changer may either consist in areturn of the constituent parts thereof to their original positionsindicated in FIG. 4, which is a reversal of the operation which has beenpreviously described in detail, or the next operation of the load tapchanger may consist in a switching operation from taps number eight ofselector switches 3t 31, 32 to taps number nine thereof. The lastmentioned operation is a duplication of the switching operation whichhas been described above, i.e. a switching operation from taps numberseven of selector switches 31), 31, 32 to taps number eight thereof.

Provision of reversal switch 54 makes it possible to reduce the numberof taps of center winding 1% for a given or predetermined control dutysince it makes it possible to use the voltage in the tapped centerwinding 1% selectively either for the purpose of boosting or for thepurpose of bucking.

It will be apparent from the foregoing that a polyphase load tap changerembodying the present invention comprises a plurality of substantiallyidentical transfer switches 15, 16, 17 each connected into one phase ofa polyphase circuit and superimposed in substantially coaxial relationto form a transfer switch stack. The transfer switches comprised in saidstack are angularly displaced a number of degrees equal to 360 dividedby the number of the phases of the polyphase transformer. As a result ofthis angular displacement the hot products of arcing formed at loadcurrent switching operations of the transfer switches which are arrangedat relatively low levels of the aforementioned stack are substantiallykept away from the arcing zones of the transfer switches which arearranged at relatively high levels of the aforementioned stack. Theparticular embodiment of the invention described above is a load tapchanger for a three phase transformer and its transfer switch stackcomprises three transfer switches. The three transfer switches areangnlarly displaced 360:3:120 degrees, as best shown in FIGS. 3a, 3b and3c. The aforementioned an gular displacement of the constituent transferswitches 15, 16, 17 of the transfer switch stack is generally sufificiently effective to provide for a rapid dielectric recovery of theionized gaps formed between the parting contacts of transfer switches15, 16, 17. If desired baffles may be provided between the variouslevels of a stack of transfer switches to keep the hot products ofarcing of one transfer switch away from the arcing zone of the othertransfer switches and to control the upward fiow of products of arcingin a predetermined desired fashion.

The aforementioned angular displacement of transfer switches 15, 16, 17,i.e. of the sets of fixed contacts 21 and the sets of movable contacts19 thereof makes it necessary to angularly displace the tap-changingresistors 24 in the same fashion. This has been clearly shown in FIGS.3a-3c in which structure the tap-changing resistors 24 of transferswitches 15, 16, 17 are angularly displaced 120 degrees.

It appears further from the foregoing that each of the transfer switches15, 16, 17 of polyphase load tap changers embodying the presentinvention includes a plurality of fixed circularly arranged contacts 21,a set of movable contacts 19 and current-limiting tap change resistors24 within the cylindrical space defined by said circularly arrangedfixed contacts 21.

The present invention contemplates the use of transfer switches of thegeneral type disclosed and claimed in United States Patent 2,680,790 toB. Jansen, Load Changeover Switch for Tapped Transformers Using aCombination of Contact Movements, June 8, 1954 and United States Patent2,833,873 to B. Jansen, Multi-Pole Tap Switch for Changing TransformerTaps Under Load, May 6, 1958, and reference may be had to the twoaforementioned patents as to further details in regard to the transferswitches intended to be used for carrying the present invention intoeffect.

Load tap changers embodying the present invention further compriseinsulating means for insulating the constituent transfer switches 15,16, 17 of the transfer switch stack in accordance with the voltageprevailing between phases. The aforementioned insulating means includethe body of oil inside of vessel 11 in which the transfer switches 15,16, 17 are immersed, and the aforemen tioned insulating means furtherinclude the common shaft 13 for jointly operating the constituenttransfer switches 15, 1d, 17 of the transfer switch stack which shaft isat least in part of insulating material.

it appears also from the foregoing that load tap secutive or contiguoustaps.

changers embodying the present invention comprise a plurality ofsubstantially identical selector switches 39, 31, 32 each connected intoone phase of a polyphase circuit and superimposed in substantiallycoaxial relation to form a selector switch stack arranged in proximityof, or immediately adjacent to, the aforementioned transfer switchstack. The vertical spacing of the constituent transfer switches of thetransfer switch stack and the vertical spacing of the constituentselector switches of the selector switch stack is substantially equal.Hence each transfer switch and each selector switch pertaining to thesame phase are situated at substantially the same level, and eachtransfer switch is operatively related to one of the selector switchesby leads 33, 34, 35 which are substantially horizontal or, in otherwords, do not extend beyond the two horizontal planes which form theupper and the lower boundary of a pair of associated and cooperativelyrelated transfer switches and selector switches. These leads are,therefore, arranged in equipotential spaces, i.e. spaces throughoutwhich there is substantially the same potential. To be more specific,the required insulation of the leads 33, 34, 35 between cooperatingtransfer switches and selector switches is but that called for by thedifference in voltage between con- This is a minimum of insulationrequirement. The tap change resistors 24 for limiting the flow ofcirculating currents incident to changing from one tap to another arepreferably arranged within the above equipotential areas, formingintegral parts of the transfer switches 15, to, 17 to which they areoperatively related. The gear means for operating the transfer switches15, 16, 17 and for operating the selector switches 39, 31, 32 arearranged on top of the transfer switch stack and on top of the selectorswitch stack.

It will also be apparent from the foregoing that the leads 33, 34, 35operatively relating the transfer switch and the selector switchpertaining to the same phase do not cross with like leads operativelyrelating transfer switches and selector switches of other phases.

It is a feature inherent in the above described structure that theconstituent switches 15, 16, 17 of the transfer switch stack and theconstituent switches 39, 31, 32 of the selector switch stack may jointlybe insulated against ground, which results in much more economical andcompact structures than where cooperating pairs of transfer switches andselector switches are separately insulated against ground. Since theimpulse strength of insulation against ground must be relatively high,this feature is one which is of considerable importance.

The common drive means for all transfer switches 15, 16, 17 and for allselector switches 30, 31, 32 of the load tap changer is a featuregreatly reducing prime cost and space requirements. Since the volume ofoil involved for insulating load tap changers embodying this inventionis relatively small, and since inspection of the aforementioned commondrive and of the switches integrated into the transfer switch stack andof the switches integrated into the selector switch stack is relativelysimple, the cost of maintenance of load tap changers embodying thepresent invention are minimized.

Load tap chargers embodying this invention lend themselves to manual aswell as to automatic supervisory control.

It will be understood that although but one embodiment of the inventionhas been illustrated and described in detail, the invention is notlimited thereto. It will also be understood that the structureillustrated may be modified without departing from the spirit and scopeof the invention as set forth in the accompanying claims.

It is claimed:

1. A load tap changer for polyphase transformers comprising incombination with a plurality of tapped phase windings of a polyphasetransformer:

(a) a horizontal cover plate;

(b) an oil filled cylindrical vessel attached to said plate ranged fixedcontacts engageable by said pair of and projecting from the lowersurface thereof; rotary contacts, each of said plurality of fixed con-(c) a plurality of stacked transfer switches each artacts of each ofsaid plurality of selector switches ranged within said vessel in coaxialrelation thereto, being conductively connected to one tap of one of eachof said plurality of transfer switches including 5 said plurality of.phase windings, and said pair of fixed contacts and movable contactscooperating with rotary contacts of each of said pair of selector saidfixed contacts in a predetermined sequence; switches being conductivelyconnected to said second (d) a shaft coextensive with the axis of saidvessel end of said constituent resistors of one of said pluprojectingtransversely through said cover plate for rality of groups of resistors.joint operation of said plurality of transfer switch s; 19 3. A loadta-p changer for polyphase transformers com- (e) a plurality of groupsof resistors arranged Within prising in combination with a plurality oftapped phase said vessel each at substantially the same level as onewindings of a polyphase transformer: of said plurality of transferswitches, the constituent (a) a plurality of stacked transfer switcheseach inresistors of each of said plurality of groups of recluding fixedcontacts and movable contacts cosistors having a first end conductivelyconnected operating with said fixed contacts in a predetermined to someof said fixed contacts of one of said pluralsequence; ity of transferswitches and the constituent resistors (1;) a ti l haft forgang-operating id l lit of each of Said plurality 6f groups of resistors113V" of transfer switches including insulating means for ing a secondend; insulating said plurality of transfer switches from (f) a pluralityof stack selector switches each arranged 20 h th at substantially thesame level as one of said plurality a plurality of stacked groups ofresistor h of transfer wit d One Of Said plurality of ranged atsubstantially the same level as one of said groups of resistors, each ofSaid plurality of Selector plurality of transfer switches, theconstituent resis- SWllIClli-ZS including 21 pair Of rotary contacts,and each tors f each of said plurality of groups of resistors of Saidplurality of Selector Switches including 3 p 25 having a first endconductively connected to some il 0f circularly arranged fixed ccflmctsengageable of said fixed contacts of one of said plurality of y Said Pof TOtaYY Contacts, each of Said plurality transfer switches and theconstituent resistors of each of fixed contacts of each of saidplurality of selector f said prurarity f gmups f resistors having aswitches being conductively connected to one tap of d d; 0116 Of Saidplurality of Phase windings, and Said (d) a plurality of stackedselector switches each ar- P of rotary Contacts of each 0f Said P of5615C- ranged at substantially the same level as one of said torswitches being conductively connected to said plurality f t n f r i hand one of id 1 second end of said constituent resistors of one of saidm f groups f resistors, h f i 1 1i g plurality of groups f TeSiStOYS;selector switches including a pair of rotary contacts, (8) an insulatingcolumn Parallel to Said Shaft P and each of said plurality of selectorswitches infulcra for said pair Of I'OtZlIy contracts Of Each aplurality of circularly arranged fixed on of said plurality of selfictofSwitches; and tacts engageable by said pair of rotary contacts, each (h)drive means for said plurality of transfer switches f Said m m f fixgdContacts of h of i and for Said plurality of Selector Switches PPplurality of selector switches being conductively cony Said Cover Plate,Said drive maans including a 4" nected to one tap of one of saidplurality of phase loaded Operating Spring arranged abflve Said Coverwindings, and said pair of rotary contacts of each Plate for OperatingSaid first Shaft and a Geneva gear of said pair of selector switchesbeing conductively dIiW for gang Opfifatifig Said P of rotary Contactsconnected to said second end of said constituent reof each of Said p yof Selector SWilChQS- sistors of one of said plurality of groups ofresistors; A 10215 p Changer for P yp transfflfmers C0111" (e) avertical insulating column in the center of said p in Combination With aplurality of pp Phase a plurality of selector switches providing fulcrafor windings Of 51 1 311 transformer: said pair of rotary contacts ofeach of said plurality (a) an oil filled substantially cylindricalvessel; f glegtor it h an insulating Cylinder arranged inside Saidvessel (3) additional vertical insulating columns providing in coaxialrelati n h 'w; 5O mechanical ties between each of said pair of rotary aplurality of Stacked transfer Switchfis each contacts of each of saidplurality of selector switches;

ranged within said vessel in coaxial relation thereto, and each of saidplurality of transfer switches including a Geneva gear d i arrangedabove id l lit fixed contacts and movable contacts cooperating with fsalector i h tiv ly engaging b upper said fiXcd Contacts in apredetermined Sequence, 55 ends of said additional insulating columnsfor gang said fixed contacts of each of said plurality of transoperatingsaid plurality of selector switches.

fer switches being supported by said insulating cylinder;

(d) a plurality of groups of current-limiting resistors arranged withinthe space bounded by said insulating 4. A load tap changer for polyphasetransformers comprising in combination with a plurality of tapped phasewindings of a polyphase transformer:

69 (a) a plurality of stacked, jointly operable rotary seleccylindereach arranged at substantially the same level as, one of said pluralityof transfer switches, the constituent resistors of each of saidplurality of groups of resistors having a first end conductivelyconnected to some of said fixed contacts of one of tor switcheselectrically insulated from each other, each being at a predeterminedpotential, each of said plurality of selector switches including aplurality of circularly arranged fixed contacts each connected to one ofthe taps of one of said plurality of tapped said plurality of transferswitches and the constituent Phase windings of said transformer and eachof said resistors each of Said plurality of groups of plurality ofselector switches further including a pair SiStOIS having a Second andor" movable contacts each cooperating with said (e) a plurality ofstacked rotary selector switches each plurality of fixed contacts;

arranged at substantially the same level as one of said 70 (b) a m m ofsmacked jointly opgmble namfer plurality 0f transfer Switches and one 0fsaid P switches electrically insulated from each other, each ity ofgroups of current-limiting resistors, each of b i t a predecerminedpotential, each of said plusaid plurality of selector switches includinga pair rality of transfer switches having a plurality of cirof rotarycontacts, and each of said plurality of seleccularly arranged fixedcontacts including outer main tor switches including a plurality ofcircularly ar 7 contacts and inner auxiliary contacts and each of saidplurality of transfer switches further having a plurality of movablecontacts each cooperating in a predetermined sequence with one of saidplurality of fixed contacts, each of said plurality of transfer switchesbeing arranged at substantially the same level as one of said pluralityof selector switches being at the same potential; and

c a luralit of rou s of switchin resistors the constituent resistors ofeach of said plurality of groups of switching resistors having a firstend and having a second end and being connected with said first end.thereoi to said pair of movable contacts of one of said plurality ofselector switches, and being connected with :said second end thereof tosaid fixed auxiliary contacts of one of said plurality of transferswitches, and each of said plurality of groups of switching resistorsbeing arranged at substantially the same level as one of said pluralityof selector switches and one of said plurality of transfer switches.

comprising in combination with a plurality of tapped phase windings of athree phase transformer:

(a) a plurality of stacked jointly operable rotary se- V lector switcheselectrically insulated from each other and at different potentials, eachof said plurality of selector switches having circularly arranged fixedcontacts conductively connected to the taps of one of Said plurality ofphase windings of said transformer and a pair of movable contactscooperating with said fixed contacts;

(b) a plurality of groups of stacked switching resistors having aspacing substantially equal to the spacing of said plurality of selectorswitches, the constituent resistors of each of said plurality of groupsof switching resistors having a first end and having a second end andbeing conductively connected with said first end thereof to said pair ofmovable contacts of one of said plurality of selector switches; and

(c) a plurality of stacked jointly operable rotary trans- 5. A load tapchanger for polyphase transformers corne prising in combination with aplurality of tapped phase windings of a polyphase ransformer:

(a) a plurality of stacked jointly operable rotary selecfer switcheselectrically insulated from each other and at different potentials, eachof said plurality of transfer switches having a plurality of circularlyartor switches electrically insulated from each other and at differentpotentials, each of said plurality of selector switches having aplurality of circularly arranged fixed contacts each connected to one ofthe taps of one of said plurality of phase win-dings of said transformerand each of said plurality of searranged fixed contacts including outermain contacts and inner auxiliary contacts and each of said plurality oftransfer switches further having a plurality of movable contactscooperating in a predetermined sequcnce with one of said plurality offixed contacts, each of said plurality of transfer switches beingarranged at substantially the same level as one. of said plurality ofselector switches;

(d) means for controlling the voltage distribution along the stackformed by said plurality of transfer switches ranged fixed contactsincluding outer main contacts and inner auxiliary contacts and eachhaving an equal number of movable contacts cooperating in apredetermined sequence with said fixed contacts, said plurality oftransfer switches having a spacing substantially equal to the spacing ofsaid plurality of selector switches and said fixed auxiliary contacts oflectof hailing P movabla com'acts each of said plurality of transferswitches being cone'ach wlth Sam plurality of fixed Comm; ductivelyconnected to said second end of said constit- (b) means for controllingthe voltage distribution along uent resistors of one of Said pluralityof groups of Stack foamed by Said plurality of semen switches switchingresistors, said plurality of fixed contacts tending to @Smabush ofequitlolemial Zoms and said movable contacts of each of said pluralityeallh Occupied by Om of Sand mummy of Selector of transfer switchesbeing angularly displaced 120 Swltchfls; degrees and encompassing anangle of less than 180 (c) plumhty 1 stacked iomtly Can-Mable transferdegrees, each of said plurality of groups of switching switcheselectrically 1nsulated from each other each resistors bang arrangedimmediately adjacent Said being at a different pawl-M131 each of Sand it lurality of fixed contacts and immediately adiacent of transferswitches having a plurality of circularly 49 g said movable contacts ofone of Said plural'ity of transfer switches and angularly displaced 120degrees.

7. A load tap changer as specified in claim 6 comprising a commonvertical shaft for jointly operating said plurality of transferswitches, said shaft comprising insulating sections alternating withmetallic sections, each of said insulating sections being arrangedbetween contiguous of said plurality of transfer switches and each ofsaid metallic sections being substantially coextensive with 50 the heiht of one of said luralit of transfer switches. wndmg egtabhshplulr'ahty o'fpeqmplotemmal Zonfis 8. A load tap changer fofpolypli asetransformers coml g i Led one of smd pummy of {mm/fen. prising incombination with a plurality of tapped phase f windings of a polyphasetransformer:

(e) a i p gmd'ps Of i i i' (a) a plurality of stacked jointly operablerotary selecsmd mummy Of glllpsofswlichmg reslsltors banig tor switcheselectrically insulated from each other i at i 2 i of d and at differentpotentials, each of said plurality of phlarhty P i regsselector switcheshaving circularly arranged fixed of each of Sald plurality of gsqups ofSwitching contacts conductively connected to the taps of one resistors hving a first end and having a seE-ond end of Said plurality of phqsewindings of said trans t v 1 p S U L, r v I c L c I i Q befmg i f Qaldfirst .i e Of.to former and a pair of movable contacts cooperating uafiked l contacts of ahty with sa d fixed contacts of transferswitchesand b a luraht of rou s of current-limitm 1m ed- (f) of i l g ii g i g zinces each if said plufality of groups of imiedaiices pairs oea s,eac o sat puraty o pair's o ea s b in If n ed t bt H c s the samelevel as one conductively connecting said pair 01. movable con- 7, e a ga an m taots of one of said plurality of selector switches 4:0 giggigg ggi i g g g 2 5 ;5 1:2 2; said second end of the constituent resistors ofone impndances having a first end ,md gi a second of mad mummy i l f g iend and being conductively connected with said first and each 531d fpjaus end thereof to said pair of movable contacts of one arnauged inone of said plurality of equipotential of Said plurality of selactorswitches;

ZQHES P- {me f said plurality f (c) cylindrical contact supporting meansof insulating switches and in one of said plurality of equipotentlal il; and

limes p' y One of Said Plumli'iy 01f mimfel (d) a plurality of stackedjointly operable rotary transswitches. fer switches electricallyinsulated from each other 6. A load tap changer for three phasetransformers and at different potentials, each of said plurality of reltransfer switches having a plurality of circularly arranged fixedcontacts including outer main contacts and inner auxiliary contactssupported by said cylindrical contact supporting means and each havingmovable contacts cooperating in a predetermined sequence with said fixedcontacts, each of said plurality of transfer switches being arranged atsubstantially the same level as one of said plurality of selectorswitches and one of said plurality of groups of irnpedances, said fixedauxiliary contacts of each of said plurality of transfer switches beingconductively connected to said second end of said constituent impedancesof one of said plurality of groups of impedances, said plurality oftransfer switches being angularly displaced a number of degreessubstantially equal to 360 divided by the number of phases of saidpolyphase transformer.

References Cited in the file of this patent UNITED STATES PATENTS VonZweigbergk Sept. 20, Sessions Sept. 26, Koontz Feb. 13, Jansen Jan. 1,Le Count Aug. 19, Jansen June 8, Jansen Oct. 5, Jansen Nov. 8, JansenMay 6,

FOREIGN PATENTS France Apr. 24,

1. A LOAD TAP CHANGER FOR POLYPHASE TRANSFORMERS COMPRISING INCOMBINATION WITH A PLURALITY OF TAPPED PHASE WIDNINGS OF A POLYPHASETRANSFORMER: (A) A HORIZONTAL COVER PLATE: (B) AN OIL FILLED CYLINDRICALVESSEL ATTACHED TO SAID PLATE AND PROJECTING FROM THE LOWER SURFACETHEREOF; (C) A PLURALITY OF STACKED TRANSFER SWITCHES EACH ARRANGEDWITHIN SAID VESSEL IN COAXIAL RELATION THERETO, EACH OF SAID PLURALITYOF TRANSFER SWITCHES INCLUDING FIXED CONTACTS AND MOVABLE CONTACTSCOOPERTING WITH SAID FIXED CONTACTS IN A PREDETERMINED SEQUENCE; (D) ASHAFT COEXTENSIVE WITH THE AXIS OF SAID VESSEL PROJECTING TRANSVERSELYTHROUGH SAID COVER PLATE FOR JOINT OPERATION OF SAID PLURALITY OFTRANSFER SWITCHES; (E) A PLURALITY OF GROUPS OF RESISTORS ARRANGEDWITHIN SAID VESSEL EACH AT SUBSTANTIALLY THE SAME LEVEL AS ONE OF SAIDPLURALITY OF TRANSFER SWITCHES, THE CONSTITUENT RESTORS OF EACH OF SAIDPLURLITY OF GROUPS OF RESITORS HAVING A FIRST END CONDUCTIVELY CONNECTEDTO SOME OF SAID FIXED CONTACTS OF ONE OF SAID PLURALITY OF TRANSFERSWITCHES AND THE CONSTITUENT RESISTORS OF EACH OF SAID PLURLAITY OFGROUPS OF RESITORS HAVING A SECOND END; (F) A PLURLAITY OF STACKSELECTOR SWITCHES EACH ARRANGED AT SUBSTANTIALLY THE SAME LEVEL AS ONEOF SAID PLURALITY OF TRANSFER SWITCHES AND ONE OF SAID PLURALITY OFSELECTOR GROUPS OF RESISTORS, EACH OF SAID PLURALITY OF SELECTORSWITCHES INCLUDING A PAIR OF ROTARY CONTACTS, AND EACH OF SAID PLURLAITYOF SELECTOR SWITCHES INCLUDING A PLURALITY OF CIRCULARLY ARRANGED FIXEDCONTACTS ENGAGEABLY BY SAID PAIR OF ROTARY CONTACTS, EACH OF SAIDPLURALITY OF FIXED CONTACTS OF EACH OF SAID PLURALITY OF SELECTORSWITCHES BEING CONDUCTIVELY CONNECTED TO ONE TAP OF ONE OF SAIDPLURALITY OF PHASE OF WINDINGS, AND SAID PAIR OF ROTARY CONTACTS OF EACHOF SAID PAIR OF ELECTOR SWITCHES BEING CONDUCTIVELY CONNECTED TO SAIDSECOND END OF SAID CONSTITUENT RESISTORS OF ONE OF SAID PLURALITY OFGROUPS OF RESISTORS; (G) AN INSULATING COLUMN PARALLEL TO SAID SHAFTPROVIDING FULCRA FOR SAID PAIR OF ROATARY CONTACTS OF EACH OF SAIDPLURLAITY OF SELECTOR SWITCHES; AND (H) DRIVE MEANS FOR SAID PLURLAITYOF TRANSFER SWITCHES AND FOR SAID PLURALITY OF SELECTOR SWITCHESSUPPORTED BY SAID COVER PLATE, SAID DRIVE MEANS INCLUDING A LOADEDOPERATING SPRING ARRANGED ABOVE SAID COVER PLATE FOR OPERATING SAIDFIRST SHAFT AND A GENEVA GEAR DRIVE FOR GANG OPERATING SAID PAIR OFROTARY CONTACTS OF EACH OF SAID PLURALITY OF SELECTOR SWITCHES.